Cleaning apparatus for the operation of filter equipment

ABSTRACT

A filter equipment containing a number of filter units of conventional design, connected directly to process equipment, in which dust laden vapors are evolved under vacuum. Means are used to back wash, dry and heat the individual filter bags during continuous operation. The backwashing, drying and heating is performed with superheated vapor having the same composition as the vapor evolved in the main process. After condensation, part of the vapor evolved in the main process may be diverted into an evaporator, superheated in the vapor phase and then used for the backwashing, drying and heating. If lines are too long resulting in vapor near the dew point, the effect of double expansion with partial condensation may be used to bring back the vapor to the superheated phase before backwashing a filter bag.

Umted States Patent [151 3,704,573

Koller et al. Dec. 5, 1972 [54] CLEANING APPARATUS FOR THE 3,473,30010/1969 Wilm et al. ..55/343 OPERATION OF FILTER EQUIPMENT 3,535,852 10/1970 Hirs ..55/527 2 237 417 4/1941 Groft ..55/282 72 l t .HansKoll U F-Portne both 1 men ms g 'i i 3,538,615 10/1970 Fuhring ..34/74 [73]Assignee: Buss AG, Basel, Switzerland p i Emminer ;Bemard Nozick [22]Filed: Sept. 8,1970 Att0mey Abraham A. Saffitz [2]] Appl. No.: 70,162[57] ABSTRACT A filter equipment containing a number of filter units[30] Fol-mg Apphcat'on Pnonty Data of conventional design, connecteddirectly to process Sept. 9, 1969 Austria ..A 8540/69 equipment, inwhich dust laden vapors are evolved under vacuum.

[52] Means are used to back wash, dry and heat the in- [51] Int Cl Hnold 46/04 dividual filter bags during continuous operation. The 58Field of Search ..210/333, 167; 55/96, 262, 302, backwashmg drymg 'iheatmg 55 B43, 341 283; 34/74, 82; 202/200; perheated vapor having thesame composition as the 203/41; 159/4 C; 68/18 F vapor evolved in themam process.

After condensation, part of the vapor evolved in the References Cltedmain process may be diverted into an evaporator, su-

UNITED STATES PATENTS perheated in the vapor phase and then used for thebackwashing, drying and heating. If lines are too long etal resulting invapor near the dew point the effect of double expansion condensation maybe 13( i 8 1i used to bring back the vapor to the superheated phase erosbefore backwashin a filter ba 3,208,205 9/1965 Harms et a1. .....55/527g g 3,352,763 11/1967 Shields ..-.....210/167 1 Claim, 1 Drawing FigureZ q-- H F-t i-- 13-; 5 15' 15 6 7 V 5 f f 2 I 5 q I 2 1 a 17 ll A i T ,s

RKTENIEBHEB 51912 INVENTORS HANS ROLLER and URS FREY-PORTNER ATT RNEYATTORNEY CLEANING APPARATUS FOR THE OPERATION OF FILTER EQUIPMENTBACKGROUND OF THE INVENTION The field of application of the presentinvention relates to the filtration of dust laden vapor which is evolvedfrom thermally sensitive substances in a vacuum dryer or an extractionplant, these dust laden vapors being evolved near the point ofcondensation. The filter has to be cleaned during this operation and thepresent invention is directed to solving this problem. It furtherrelates to reverse flow cleaning of an individual filter chamber or bagin a filter combination, in which dust ladden vapors from a vacuum dryeror an extraction plant are to be filtered and where the filter has to becleaned during operation.

Reverse flow cleaning, the so-called backwashing of individual filterunits, is well known and successfully applied where dust laden gas ispassed through the porous wall of a chamber or a bag, while the dust isleft clinging to the outer surface of the latter.

But this system has not been successfully applicable where vapors are tobe filtered in a state near the point of condensation and contaminatedwith dust. In this case part of the vapors readily condense in the poresof membranes or bag-cloth and increase the resistance the passage offurther vapor until complete blockage occurs. Often the dust combineswith the prematurely condensed vapor to form a sticky mass not easilydislodgable during cleaning operations.

If this occurs during a vacuum drying operation of thermally sensitivesubstances, costly interruptions occur and a disadvantageously prolongeddrying time results.

The present invention discloses a means to heat the individual porousmembranes of filter bags in a'filter unit in a periodic cycle withoutinterruption of the main process, thus to prevent for an appreciabletime premature condensation in the pores of the filter bags of thevapors which are to be filtered. At the same time the filter members areblown free of accumulated dust, any condensate being evaporated and themembers dryed again. Use is made for backwashing of superheated vaporhaving the same composition as the vapors evolved in the main process.

This offers the advantages of no contamination, possible use of hotcondensate for producing small quantities of superheated vapor forback-washing, same characteristics for condensation of both the processand the backwash vapor and practically no increase of load on the vacuumequipment because the amount of uncondensables will not be increased bythis apparatus.

An arrangement of means to operate the apparatus of the presentinvention is diagramatically shown on the attached drawing.

It presents the arrangement preferred in conjunction with a rotaryvacuum dryer.

Referring to the drawing and the numerals of reference thereon, therotary vacuum dryer 1 operates in a manner to evaporate solvent, thevapors of which pass through a filter unit 2, equipped with outer jacketfor heating, the heating medium entering at 3 and leaving at 3 Thefilter unit 2 is provided with the required number of filter bags 4, twoof which are shown in the sum diagram. A slide 14 may be used tocyclically divide each of the filter bags from the vacuum suction,during the time when it is blown in reverse flow with superheated vapor.If the superheated vapor is blown with high pressure as a blast, thedividing slide 14 may be obviated. If the superheated vapor is blownmore gently and for an appreciably longer time than required for dryingand heating of the bag, then the stepwise movement of the slide to thenext bag may be combined with a rapping movement to shake the just driedbag and free it of any solid still clinging to it. The exhaust line 15for the filtered vapors leads to a condenser 5, pro vided with a coolingcoil 5', the traces of uncondensable gas being then aspired by thevacuum pump 6 connected by line 16 to the condenser 5. The condensate isdischarged through pipe 17, the condenser 5 being mounted in an elevatedposition to allow discharge barometrically against the vacuum. Ifrequired, the discharge can be diverted from time to time through theremotely controlled dividing valve 8 to fill the solvent evaporator 9 toa controlled level. Heat is provided by coil 10 and evaporates thesolvent so that the superheated vapors escape through pipe 18 andaccumulate in drum 11. In number corresponding to the number of filterbags individual lines 19 and 20 or a single line with the requirednumber of branched outlets lead to the filter unit 2. A remote control12 operates valves on each branch to blow in sequence each filter bag 4and to turn the slide 14 into the next position, rapping during releasethe filter bag just blown.

The advantage of the disclosed apparatus in an embodiment according tothe described example is a substantially shorter period of drying ofthermosensitive pharmaceuticals in a rotary vacuum dryer, than requiredin the same equipment with the bag filter operated in the conventionalmanner, during which considerable increase in flow resistance throughthe filter bags gradually reduced the efficiency of the vacuum in thedryer.

It has been found possible to reduce the drying time by the applicationof the new method by 30 percent without any need for specialinterruption for bag cleaning after the charge had been dried.

What we claim is:

1. A filter cleaning means comprising a filter housing adapted to beconnected to a dryer having filter bags therein, which filter dust fromsolvent laden vapors passing through said filter bags, said filterhousing including means for passing dust laden solvent vapors throughthe filter bags in a forward flow direction, means connected to saidhousing for blowing vapor through said filter bags in reverse flowrelation to the flow of solvent laden vapor from said dryer and throughsaid bags, sliding means dividing said filter bags from each other andto permit the bags to be separately blown in said reverse flow, aheating coil means, in heat exchange relation with said filter housing,an exhaust line from said filter housing, a condenser connected to saidexhaust line including a cooling coil to condense solvent'vapors, anevaporator, valve means connected to said condenser and said evaporatorsaid condenser being mounted above said evaporator so that thecondensate is discharged barometrically against the vacuum through saidvalve means and means connected to said evaporator and to said means forblowing vapor for controlling the flow of superheated solvent to blowagainst a selected filter bag in the reverse flow direction and therebyclean the filter.

1. A filter cleaning means comprising a filter housing adapted to beconnected to a dryer having filter bags therein, which filter dust fromsolvent laden vapors passing through said filter bags, said filterhousing including means for passing dust laden solvent vapors throughthe filter bags in a forward flow direction, means connected to saidhousing for blowing vapor through said filter bags in reverse flowrelation to the flow of solvent laden vapor from said dryer and throughsaid bags, sliding means dividing said filter bags from each other andto permit the bags to be separately blown in said reverse flow, aheating coil means, in heat exchange relation with said filter housing,an exhaust line from said filter housing, a condenser connected to saidexhaust line including a cooling coil to condense solvent vapors, anevaporator, valve means connected to said condenser and said evaporatorsaid condenser being mounteD above said evaporator so that thecondensate is discharged barometrically against the vacuum through saidvalve means and means connected to said evaporator and to said means forblowing vapor for controlling the flow of superheated solvent to blowagainst a selected filter bag in the reverse flow direction and therebyclean the filter.